The basic processes for obtaining useful color images from exposed color photographic silver halide materials include several steps of photochemical processing such as color development, silver bleaching, silver halide fixing and water washing or dye image stabilizing using appropriate photochemical compositions.
Photographic color developing compositions are used to process color photographic materials such as color photographic films and papers to provide the desired dye images early in the photoprocessing method. Such compositions generally contain color developing agents, for example 4-amino-3-methyl-N-(2-methane sulfonamidoethyl)aniline, as reducing agents to react with suitable color forming couplers to form the desired dyes. U.S. Pat. No. 4,892,804 (Vincent et al.) describes conventional color developing compositions that have found considerable commercial success in the photographic industry. Other known color developing compositions are described in U.S. Pat. No. 4,876,174 (Ishikawa et al.), U.S. Pat. No. 5,354,646 (Kobayashi et al.) and U.S. Pat. No. 5,660,974 (Marrese et al.).
It is common practice to add a “replenishing” solution to the color developing composition in the processing machine in order to replace photochemicals that are depleted during reaction or carried away by the processed materials. Such replenishment insures uniform development and maximum stability of the color developing agent.
Color developing compositions are commonly supplied in three or more “parts” (or solutions) that are mixed immediately before use. Multiple parts are often required in order to separate and preserve the chemical activity and solubility of components that may otherwise deteriorate or react with each other when they are stored together for long periods of time under alkaline conditions. For example, one part might include a color developing agent. Another part might contain agents to preserve the alkalinity of the mixed color developing composition. Still another part may include an optical brightener. Upon combination of all parts and water, a homogeneous color developing composition can usually be obtained for the working strength solution in the processing machine.
Problem to be Solved
There is a desire in the industry to reduce the number of parts used to prepare color developing compositions, and particularly to prepare replenishing solutions. A wide range of compositions is described in the art or commercially available as “ready to use” solutions, concentrates or dry formulations. Liquid concentrates have only to be diluted with water to provide a working strength solution. Dry formulations need only be dissolved in water. For example, EP 0 793,141 A1 (Chugai Photo) describes a two-part color developing composition that can be supplied in either solid or liquid form.
It is generally known that the concentrations of various photochemicals used in a photographic processing bath must lie within certain narrow limits in order to provide optimal performance. The most important solvent for such photoprocessing is water. Most inorganic salts can be readily dissolved in water while the organic photochemicals in such processing baths usually have suitable solubility in water at the desired operating concentrations.
However, water is both an asset and a major problem of ready-to-use and some concentrated photographic compositions because of its presence in high quantity. As a result, the costs of manufacturing, transport and storage of such compositions are steadily growing. Normally, the user of photochemical compositions has water available in which individual photochemicals could be mixed or diluted, but this is usually not practical for a number of reasons. The exact composition of the photochemicals is not readily determined by a common user and manufacturers are not likely to readily provide their formulations for such a purpose. Moreover, even if the formulations are known, mixing mistakes may result in poor photoprocessing results.
For these reasons, there is a trend in the photographic industry to provide photoprocessing compositions (including color developing compositions) in concentrated form. Moreover, there has been a desire in the industry to provide compositions that can be used right out of their containers without the need for mixing various components such as in what are known as “automatic replenishing” processors.
The industry has investigated the use of both concentrates and solid mixtures (including powders and tablets). In most cases, concentrates are convenient to use but may have high packaging costs compared to powders or be in the form of slurries or two-phase mixtures. Powders permit high concentration, but not every photochemical composition can be dried into a stable powder. In addition, powders present problems of dust, separate packaging needs, and more troublesome metering or mixing procedures. Not all dry processing compositions are readily dissolved in water.
The common color developing compositions used to provide color images in color negative films are typically obtained by combining three “parts” into a single solution. Currently, the conventional antioxidant, hydroxylamine sulfate, must be kept separated from sulfites until they are used in processing. Similarly, the conventional color developing agent, 4-(N-ethyl-N-β-hydroxyethylamino)-2-methylaniline sulfate (KODAK Color Developing Agent CD-4) must be kept at low pH for solubility purposes, but a low pH environment is not suitable for other essential photoprocessing chemicals.
The casual observer might consider that all of the conventional “parts” used to provide color developing compositions might be readily combined to form a single-part homogeneous composition. As one skilled in the art would know, this is not easy. Interactions among and deterioration of photochemicals are magnified in concentrated form, and the resulting action on processed photographic materials may be undesirable.
Some color developing compositions are commercially available in single-part formulations, but because of the presence of precipitates (such as in slurries) or multiple solvent phases, they require vigorous agitation or mixing before use. In addition, the presence of the precipitates or slurries may be unattractive to some users and other users may not have suitable equipment for proper agitation or mixing.
Ready-to-use color developing compositions are described in U.S. Pat. No. 5,273,865 (Loiacono et al) as useful for rapid access processing of photographic elements having high silver bromide emulsions.
A very useful single-part color developing composition that is homogeneous, concentrated, and stable is described in U.S. Pat. No. 6,077,651 (Darmon et al.). These concentrated compositions are most useful for processing color photographic papers.
U.S. Pat. No. 6,664,036 (Lowe et al.) describes useful homogeneous, single-part color developers for color negative film processing in which the color developers also contain a stabilizing charged organic co-solvent.
Glycols are useful organic co-solvents that allow all the components of color developers to be dissolved in a single part concentrate. These compositions, when diluted to working strength, contain residual glycol in significant concentration and the glycol can cause undesirable sensitometric effects particularly with color negative films. These effects are typically observed as contrast changes in one or more color records, resulting in contrast mismatches among the color records.
There is a continuing need in the photographic industry for a single-part color developing composition that is homogeneous, concentrated, stable, and useful particularly for processing color negative films without the undesirable sensitometric effects observed with some organic co-solvents. The present invention is directed to meeting this need in the art.